Input Devices - Upgrading and Repairing PCs - page 933

AT keyboard connector was renamed the “PS/2” port after the IBM PS/2 family of sys-
tems debuted in 1987. That was when the connector changed in size from the DIN to
the mini-DIN, and even though the signals were the same, the mini-DIN version became
known from that time forward as the PS/2 port.
Keyboards connected to a USB port work in a surprisingly similar fashion to those con-
nected to conventional DIN or mini-DIN (PS/2) ports after the data reaches the system.
Inside the keyboard, various custom controller chips are used by different keyboard man-
ufacturers to receive and interpret keyboard data before sending it to the system via the
USB port. Some of these chips contain USB hub logic to enable the keyboard to act as
a USB hub. After the keyboard data reaches the USB port on the system, the USB port
routes the data to the 8042-compatible keyboard controller, where the data is treated as
any other keyboard information.
This process works well after a system has booted into Windows. But what about users
who need to use the keyboard when running an older non-USB aware OS or within the
BIOSconfigurationroutine?Thatproblemissolvedbyensuringthat USB Legacy support
is present and enabled in the BIOS Setup. (See “ Advanced USB Configuration Menu ,” in
Chapter 5 , “ BIOS .”)
Typematic Functions
If a key on the keyboard is held down, it becomes typematic , which means the keyboard
repeatedly sends the keypress code to the motherboard. In the AT-style keyboards, the
typematic rate is adjusted by sending the appropriate commands to the keyboard pro-
cessor. This is impossible for the earlier PC/XT keyboard types because the keyboard in-
terface for these types is not bidirectional.
AT-style keyboards have programmable typematic repeat rate and delay parameters. You
can adjust the typematic repeat rate and delay parameters with settings in your system
BIOS (although not all BIOS chips can control all functions) or in your OS. In Windows
you can use either the MODE command or the Keyboard icon in the Control Panel. Using
either method, you can set the repeat rate from about 2cps (characters per second) minim-
umto30cpsmaximum,andthedelayfrom0.25secondsminimumto1secondmaximum.
Forthefastestkeyboardoperation,Iliketosettherepeatratetothemaximum(30cps)and
the delay to the minimum (0.25 seconds), which can be accomplished with the following
command:
MODE CON: RATE=31 DELAY=0
Likewise, slowing the repeat rate to the minimum (2cps) and increasing the delay to the
maximum (1 second) can be accomplished with the following command: